Technical Information Taps
Tap Types - Helix direction/ Helical pitch / Fluteless
The helix angle depends primarily upon the hole form, eg. Through hole , blind hole, deep blind hole, etc., but the material, eg short chips, long chips, also
has a strong influence on the direction of the helix. The following basic forms have derived during the development of taps:
Description
Illustration
1 Straight Flutes (Hand) - Suitable for through or blind holes. The flutes only have room for a small amount
of chips. The chips are not transported axially. Therefore, it is not advisable to cut deep through or blind
holes (except in short chipping materials), with this type.
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2 Straight Flutes with (Gun) – Suitable for through holes, the gun point curls the chip forward ahead of the
tap & out of the hole. Therefore, chip clogging is avoided and coolant can flow without problems.
< 1.5xD
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3 Spiral Flutes (LH Spiral, right hand cutting) – Suitable for interrupted through holes, where cross-holes
exist. The direction of the flutes, curls & transports the chips forward of the tap, similar to Gun taps (also,
opposite to RH spiral flutes). However, in applications where another hole intersects with the tapped hole,
the helical flutes maintain the pitching of the thread.
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15° Spiral Flutes (RH Spiral) – Suitable for blind holes, best suited to tough short chipping materials, up to
1.5 x D in depth. This particular tap design has no advantages for soft, and long chipping materials, especially
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over 1.5 x d 1 in depth. Due to the slow helix angle not transporting the chips well, clogging is possible.
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40° to 50° Spiral Flutes (RH Spiral) – Suitable for blind holes, best suited to long chipping materials,
the high helix angle & the direction of the flutes, curls & transports the chips back out of the hole.
This particular tap style is required to cut on reversal; therefore flute rake is required on the both front
& back flute faces.
D
5
> 1.5xD
< 1.5xD
D
6 Thredflo/Roll taps (fluteless) - Suitable for blind & through holes. This type of tap internally rolls a
thread, therefore displacing the metal rather than cutting, like the above mentioned styles. Due to torque
generated when producing roll threads, much higher machine power is required. Roll threads also
produce
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much stronger threads than cut threads, as the grain structure of the thread remains uniform through the
thread form profile. Note! Tapping drill size is not the same as a cut thread tap.
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The above basic tool types are available in different variations, which have been designed & developed in
respect to the specific materials and working conditions.
> 1.5xD
< 1.5xD
Tap Hole Types
thread exits one-sided
Through Holes
2
4
5
D
6
2
D
4
1
D
D
D
3
2
4
5
6
D
D
Upto
up to 1xD
1xD
(eg.
nut)
(e.g. nutter)
< 1.5xD
> 1.5xD
thread exits
Thread
exit one-sided
one side
Blind Holes D
4
5
6
4
D
5
6
D
4
D
5
6
4
D
D
> 1.5xD
5
6
D
Upto 1xD
(eg. nut)
thread exits one-sided
D
For blind holes, there are generally two thread runout forms used at the
bottom of the tap hole. One form has a recessed diameter at the bottom of
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the hole, and the other form has a standard runout. Other types of holes are
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respective to construction
designs, eg.
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thread exits one-sided
Upto 1xD
(eg. nut)
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a) The bore is smaller than the tap hole diameter (typical for pipes)
b) As step hole, where the following diameter (second step), is
smaller than the tap hole diameter.
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